John -
I am assuming you mean gate height?
While no expert on the 'physics' - I would adapt the gate to the rower to achieve the best rowing position for that athlete.
If the athletes are all different - but optimised for them, then IMO the set of the boat will be fine (mm difference in the height when the boat is empty would probably make a difference - but once you put the rowers in and keeping their blades horizontal I would think the difference fall away.).
James